The article “Empirical dual energy calibration (EDEC) for cone-beam computed tomography” by Philip Stenner et al., Medical Physics, Vol. 34, No. 9, p. 3630-3641 (September 2007) discloses a dual-energy computed tomography system, which generates energy projection data values corresponding to rays after having traversed an object to be imaged, wherein for each ray energy projection data values for two different energies are generated. A decomposition function, which depends on the generated energy projection data values, is used for decomposing the generated energy projection data values into base material projection data values such that for each ray two base material projection data values are determined, which correspond to two different base materials of the object to be imaged. The decomposed base material projection data values are then used for reconstructing a first base material image, which corresponds to a first base material of the object, and a second base material image, which corresponds to a second base material of the object. The decomposition function is a polynomial function, wherein the polynomial's coefficients are determined using a least squares fit based on thresholded images of a calibration phantom.
The decomposition of the initially generated energy projection data values into the base material projection data values can produce artifacts in the determined base material projection data values and, thus, in the finally reconstructed base material images. The quality of the finally reconstructed base material images can therefore be reduced.